Ionophores are materials capable of forming complexes with charged species, preferably cations. Chromophores are chemical groups which when present in a compound give color to the compound by causing a displacement of, or appearance of, absorbance bands in the visible spectrum.
The equilibrium constants for alkali metal complexation of polyethylene glycol ethers can be measured by low temperature nuclear magnetic resonance (NMR) spectroscopy by using a method which makes use of conformational biasing. "Flipped-out" ionophores, such as trans-cyclohexano pentaethylene glycol diethyl ethers for the complexation of metal ions are disclosed in the Journal of The Chemical Society, Chemical Communications 1983, page 1409, M. Raban et al. An oral presentation as to conformationally biased intramolecular charged transfer interaction was made in the Spring of 1989 at the Wayne State University, Department of Chemistry, Detroit, Mich. by D. Durocher et al which disclosed the ketal 4-methylthiophenoxy-8,8-dimethyl-[4.3.0]-bicyclo-7,9-dioxo-nonane-3-ol-3,5 -dinitro benzoate.
The addition of barium and calcium to an azulene crown ether has been reported as resulting in a shift in the UV-visible absorbance spectra of the material. Chem. Ber., 1984, 117, 2839, H. G. Lohr, F. Vogtle, H. Puff and W. Schuh. Since the donor atoms of the ionophore are not directly incorporated into the chromophore, the shift in spectra must be due to the interaction of the cation with the negatively polarized five-membered ring in the azulene moiety. This interaction serves to stabilize the ground state and destabilize the excited state.
Chromoionophores have been developed that upon complexation exhibit bathochromic shifts, in the absorption maximum of the UV-visible spectrum. For this to occur, the donor portion of the ionophore that is incorporated into the chromophore must be attached at its electron-poor end. Quinone imine ionophore shows a bathochromic shift upon the addition of metal cations. Chem. Ber. 1981, 114, 638 J. Dix and F. Vogtle. An amino azulene chromoionophore shows significant bathochromic shift upon the addition of barium with the solution turning yellow to blue-violet. Chem. Ber. 1985, 118, 256, H. G. Lohr and F. Vogtle. Another chromoionophore that exhibits a large bathochromic shift in the presence of pyridine/lithium is an azophenol crown reported in Tetrahedron Lett., 1981, 22, 4407, T. Kaneda, K. Sugihara, H. Kamiya and S. Mitsumi. On addition of lithium chloride, the yellowish solution turns deep purple. Other alkali metal cations show no change in the spectra. The material azophenol cryptand shows a high selectivity for potassium in dioxane/morpholine as reported in European patent application 8310028. The color change allows the quantitative determination of potassium in solution or in test strips. In both cases, the material forms a neutral complex with the metal ion in the presence of base.
It has been reported that the synthesis and characterization of chromogenic spherand ionophores have high affinity for alkaline metal cations. Spherand chromophores exhibit a high affinity for both potassium and sodium in 80% dioxane/20% water upon addition of 1,5-diazabicyclo[4.3.0]non-5-ene, Journal of American Chemical Society, 1988, 110, 571 D. J. Cram, R. A. Carmack and R. C. Helgeson. Cram has also reported the synthesis and characterization of mixed sphero cryptand and sphero-crown type chromogenic ionophores. Journal of American Chemical Society, 1989, 111, 6339 R. C. Helgeson, B. P. Chech, E. Schapotau, C. R. Gebauer, A. Kumar and D. J. Cram.
None of the prior art demonstrates materials that have the capability of acting as both a chromophore and an ionophore whereby the ionophore can preferentially interact with metal ions and where there is a color change in the solution of the material but where the ionophore and chromophore are spacially separated and electronically insulated and where the color change derives primarily from a conformational change attendant upon complexation.